Next generation high data rate downlink subsystems based on a flexible APSK modulator applying SCCC encoding

The resolution of on-board instruments and thus the amount of data acquired by earth observation satellites is steadily increasing. In order to cover the resulting downlink data capacity demands under consideration of the bandwidth limitations, it is necessary to maximize the downlink data rate and at the same time to utilize more bandwidth efficient modulation schemes. In 2012 the Consultative Committee for Space Data Systems (CCSDS) issued a recommendation aiming at exactly this kind of high rate applications. The usage of the CCSDS 131.2.B.1 waveforms combines serial concatenated convolutional codes (SCCC) and higher order modulation formats allowing adaptation of the transmission parameters to the channel conditions during a satellite-to-ground contact by means of variable and adaptive coding & modulation (VCM/ACM) and thus enables the user to maximize the downlink data capacity per fly-over. Tesat Spacecom has developed a High Data Rate Modulator according to the mentioned standard. The Modulator is designed for a maximum output symbol rate of 500 MBaud. The modulator is equipped with redundant high speed serial links enabling a maximum user input data rate of 2 Gbps. In order to compensate for the non-linearity of the subsequent traveling wave tube amplifier, what is essential especially for the envisaged higher order modulation schemes, the modulated signal is digitally pre-distorted. Full qualification will be achieved in 2017.